Plasma-Catalyzed, Thermally-Integrated Reformer For Fuel Cell Systems

ABSTRACT

A reformer is disclosed in one embodiment of the invention as including a channel to convey a preheated plurality of reactants containing both a feedstock fuel and an oxidant. A plasma generator is provided to apply an electrical potential to the reactants sufficient to ionize one or more of the reactants. These ionized reactants are then conveyed to a reaction zone where they are chemically transformed into synthesis gas containing a mixture of hydrogen and carbon monoxide. A heat transfer mechanism is used to transfer heat from an external heat source to the reformer to provide the heat of reformation.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent No.60/798,863 filed on May 8, 2006 and entitled Reformation of LiquidLogistic Fuels for Fuel Cell Systems.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to liquid fuel reformation and moreparticularly to systems and methods for reforming liquid fuels for usein fuel cell systems.

BACKGROUND

As a society, we often take for granted the mobility (power and range)afforded by the energy storage density of common transportation fuelssuch as gasoline, aviation kerosene, and diesel fuel. The legacyinvestment in the refueling infrastructure alone makes it apparent thatfuel cell technology capable of utilizing these existing fuels may havea distinct advantage over those restricted to high purity hydrogen orother less widely available fuels. The ability to utilize reformateproduced from these existing transportation fuels, as well as fromemerging non-petroleum based fuels such as bio-diesel, and synthetic(Fischer-Tropsch) liquids, without the need for extensive cleanup is anadvantage of solid oxide fuel cells (SOFCs).

The higher efficiency of fuel cells compared to conventional engines isone of the main characteristics motivating the development and eventualcommercialization of fuel cells. In stationary applications, utilizingnatural gas fuel, this efficiency advantage is well established.However, where liquid fuels are used, a fuel processor used to reformliquid fuel exacts a heavy efficiency penalty on a fuel cell system.Historically, the sulfur and aromatic content of transportation fuelshas made them impossible to reform using the catalytic steam reformingprocess used with natural gas systems, due to problems with “poisoning”the catalyst and carbon buildup. As an alternative, partial oxidationprocesses (e.g., POX, CPOX, ATR, etc.) have been employed, but thesealso suffer drawbacks.

Although reformed fuel or “reformate” produced by conventional partialoxidation of certain fuels typically represents about 80% of the energycontent of the fuel as measured by heating value, the use ofconventional partial oxidation processes with fuel cells results in aloss in the range of 30 to 40 percent of the electric power generationpotential of the fuel. This is primarily due to the fact that a fuelcell is not a heat engine. Rather, a fuel cell may be considered aFaradaic engine, and the Faradaic (current producing) potential of afuel cell is reduced by 4 Coulombs for each mole of O₂ introduced duringthe conventional partial oxidation process.

For example, referring to FIG. 1, in general, a prior art system 100 forproducing electricity using a feedstock fuel 106 as an input may includea reformer 102, or fuel processor 102, and a fuel cell 104. The reformer102 may receive and process a hydrocarbon feedstock fuel 106 to producesynthesis gas 112 containing a mixture of carbon monoxide and hydrogengas. This synthesis gas 112 in addition to oxygen 114 may be used by thefuel cell 104 to produce electricity 116. In certain embodiments, thefuel cell 104 may generate CO₂+H₂O 118 and heat 120 as a byproduct.

Where natural gas or methane is used as the feedstock fuel 106, areformer 102 may utilize a process such as catalytic steam reforming(CSR) to produce synthesis gas 112. This process generally involvesreacting the methane with steam in the presence of a metal-basedcatalyst to produce the desired synthesis gas 112. CSR and similarprocesses, however, are unable to reform liquid transportation fuelssuch as conventional diesel, heavy fuel oil, or jet fuel (e.g., JP-8,Jet-A, etc.). This is because the sulfur and aromatic content oftransportation fuels makes them difficult or impossible to reform usingCSR, at least in part because of problems with “poisoning” the catalystand carbon buildup. Instead, partial oxidation processes (e.g., POX,CPOX, ATR, etc.) are normally employed to reform transportation fuels.

In general, a conventional partial oxidation process may includepartially combusting a sub-stoichiometric mixture of feedstock fuel 106(which may include chains of —CH₂— groups, or more generally CH_(n)groups) and an oxidant 108. The combustion reaction is exothermic andprovides heat 110 utilized in reforming the remaining fuel 106 togenerate synthesis gas 112, the reformation reaction of which isendothermic. The heat of reformation is on the order of 30 percent ofthe heat generated by completely combusting the fuel 106, which can beobtained by partially combusting the fuel. Where fuels 106 are high insulfur content, partial oxidation reactors may employ non-catalyticpartial oxidation of the feed stream 106 with oxygen 108 in the presenceof steam at temperatures exceeding 1200° C.

The stoichiometric reformation reaction occurring at the reformer 102and using oxygen 108 as the oxidant may be represented generally asfollows:

—CH_(n)—+(1/2)O₂→CO+(n/2)H₂

At the fuel cell 104, the synthesis gas 112 and oxygen 114 is convertedto electricity 116, carbon dioxide 118, and steam 118 in accordance withthe following equation:

CO+H₂+O₂→CO₂+H₂O+4e⁻

As can be observed from the above equations, each CH₂ group generatesabout 4e⁻ (4 electrons) of electricity using a conventional partialoxidation reformer.

Conventional partial oxidation techniques exact a heavy efficiencypenalty on the fuel cell 104. The Faradaic (current producing) potentialof a fuel cell 104 is reduced by 4 coulombs for each mole of oxygen 108introduced in the partial oxidation process. Thus, the oxidant inconvention systems reduces the ability of the fuel cell to produceelectricity.

In view of the foregoing, what are needed are an improved system andmethod for generating reformate from various fuels that improve theFaradaic efficiency of fuel cells, such as solid oxide fuel cells(SOFCs), molten-carbonate fuel cells (MCFCs), or phosphoric acid fuelcells (PAFCs). Such a system and method would be capable of reformingfuels with high sulfur content (e.g., 10,000 ppm) without requiringsulfur pre-removal, while avoiding problems such as “poisoning” thecatalyst or carbon buildup. Further needed is an improvement to theoverall efficiency of fuel reformation and electricity production.

SUMMARY OF THE INVENTION

Consistent with the foregoing and in accordance with the invention asembodied and broadly described herein, a reformer is disclosed in oneembodiment of the invention as including a channel to convey a preheatedplurality of reactants containing both a feedstock fuel and an oxidant.A plasma generator is provided to apply an electrical potential to thereactants sufficient to ionize one or more of the reactants. Theseionized reactants are then conveyed to a reaction zone where they arechemically transformed into synthesis gas containing a mixture ofhydrogen and carbon monoxide. A heat transfer mechanism is used totransfer heat from an external heat source to the reformer to providethe heat of reformation. The reformation reaction may occur in thetemperature range of between about 350° C. and about 1100° C.

In selected embodiments, the feedstock fuel comprises at least one of ahydrocarbon and a carbon. In other words, the feedstock fuel may includea hydrocarbon and/or a carbon fuel, which may be provided in the form ofa gas, liquid, or solid. The oxidant may include at least one oxidantchosen from steam, oxygen, air, or some other oxygen-containing compoundor mixture. In selected embodiments, the reactant mixture may bevaporized or gasified in order to be processed by the reformer.

In certain embodiments, the plasma generator generates a glidingelectric arc to ionize the reactants. Similarly, the reaction zone may,in certain embodiments, include a reaction bed to homogenize thereactants by mixing, chemical buffering, or a combination thereof. Inother embodiments, the reaction zone comprises a reaction bed containingcatalysts to promote equilibration of reactive species at temperatureslower than the temperature of reformation.

In selected embodiments, the external heat source is a solid-oxide fuelcell, a molten-carbonate fuel cell, a phosphoric acid fuel cell, aFischer-Tropsch process, or the like. In one embodiment, the reformerand fuel cell are disposed within an insulated enclosure to provide heattransfer therebetween. Heat may be transferred by way of radiation,convection, or a combination thereof.

In another aspect of the invention, a thermally integrated system forproducing electricity using a feedstock fuel as an input includes aplasma reformer configured to reform a mixture containing a feedstockfuel and an oxidant. The reformate includes synthesis gas containing amixture of hydrogen and carbon monoxide gas. The reaction producing thismixture has associated therewith a heat of reformation. A fuel cell isprovided to chemically convert the synthesis gas to electricity andheat. A heat transfer mechanism is provided to transfer the heat fromthe fuel cell to the plasma reformer to provide the heat of reformation.

In another aspect of the invention, a method for increasing the Faradaicefficiency of a fuel cell includes preheating a mixture of reactantscontaining a feedstock fuel and an oxidant. An electrical potential isapplied to the reactants to ionize one or more of the reactants. Whileproviding heat of reformation, these ionized reactants are chemicallytransformed into synthesis gas containing a mixture of hydrogen andcarbon monoxide. This synthesis gas may then be used as a fuel togenerate electricity and heat. All or a portion of the heat generatedmay be transferred to the reactants to provide the heat of reformation.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited features andadvantages of the present invention are obtained, a more particulardescription of apparatus and methods in accordance with the inventionwill be rendered by reference to specific embodiments thereof, which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the present invention and are not,therefore, to be considered as limiting the scope of the invention,apparatus and methods in accordance with the present invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is a high-level block diagram of one prior art system forgenerating synthesis gas for a fuel cell;

FIG. 2 is high-level block diagram of one embodiment of a system inaccordance with the invention, providing improved synthesis gasproduction;

FIG. 3 is a high-level block diagram of one embodiment of a reformer inaccordance with the invention, integrated with a fuel cell;

FIG. 4 is a high-level block diagram of one embodiment of a reformer inaccordance with the invention;

FIGS. 5A through 5C are several schematic profile views of an embodimentof a gliding arc plasma generator;

FIG. 6 is a high-level block diagram of a thermally integrated reformerand fuel cell;

FIG. 7 is a cutaway schematic view of one embodiment of a reformer inaccordance with the invention;

FIGS. 8A through 8C are several perspective views of various componentsof a reformer in accordance with the invention;

FIGS. 9A and 9B are perspective views of other components of a reformerin accordance with the invention; and

FIG. 10 is a high-level block diagram of one embodiment of a reformerintegrated with a Fischer-Tropsch or methanation process and used togenerate synthetic fuel.

DETAILED DESCRIPTION OF THE INVENTION

It will be readily understood that the components of the embodiments asgenerally described and illustrated in the Figures herein could bearranged and designed in a wide variety of different configurations.Thus, the following more detailed description of various embodiments, asrepresented in the Figures, is not intended to limit the scope of thepresent disclosure, but is merely representative of various embodiments.While the various aspects of the embodiments are presented in drawings,the drawings are not necessarily drawn to scale unless specificallyindicated.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussion of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize that theinvention can be practiced without one or more of the specific featuresor advantages of a particular embodiment. In other instances, additionalfeatures and advantages may be recognized in certain embodiments thatmay not be present in all embodiments of the invention.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

In the following description, numerous specific details are presented toprovide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventioncan be practiced without one or more of the specific details, or withother methods, components, materials, and so forth. In other instances,well-known structures, materials, or operations such as vacuum sourcesare not shown or described in detail to avoid obscuring aspects of theinvention.

Referring to FIG. 2, in general, to overcome the efficiency penalty ofthe above-mentioned reformers, an improved system 200 in accordance withthe invention may include a sulfur-tolerant reformer 202 capable ofreforming feedstock fuels 204 with high sulfur content (e.g., greaterthan 50 ppm sulfur content) to generate synthesis gas 206. Thissynthesis gas 206 may be utilized by a synthesis gas consuming process208, such as a fuel cell 104 or other device or process which consumessynthesis gas 206, which also generates heat 210 as a byproduct. Atleast some of the heat 210 from the consuming process 208 may betransferred to the reformer 202 where it may be used to drive thesynthesis gas generating reaction, improving the yield of synthesis gas206 from the reformer 202 and the overall efficiency of the system 200.

Referring to FIG. 3, one embodiment of a system 300 functioning inaccordance with the system 200 described in FIG. 2 may include a plasmareformer 302 and a fuel cell 304 generating heat 306 as a byproduct. Inselected embodiments, the fuel cell 304 is a solid oxide fuel cell,molten carbonate fuel cell, or other fuel cell which operates at hightemperatures (e.g., greater than 600° C.). As will be explained in moredetail hereafter, the plasma reformer 302 may be used to reform fuels308 with high sulfur content without the problems associated withcatalyst poisoning or carbon buildup. Thus, the plasma reformer 302 maybe suitable to reform high-sulfur, liquid transportation fuels such asdiesel, heavy fuel oil, or jet fuel.

Heat 306 generated by the fuel cell 304 may be transferred to thereformer 302 to provide heat of reformation to the reactants 308, 310.This may reduce or eliminate the need to combust a portion of the fuel308 to provide heat of reformation since it is provided by the fuel cell304. Consequently, the amount of oxygen 108 used as the oxidant (asdescribed in FIG. 1) and used to combust the fuel 308, may be reduced ormostly eliminated and replaced with steam 310. The substitution of steam310 makes the reaction endothermic, but produces an additional H₂molecule which provides additional fuel to the fuel cell 304. As usedthroughout this application, “heat of reformation” includes heatutilized by the endothermic reformation reaction. “Reformation reaction”may also be referred to as the conversion of feedstock fuel and anoxidant into a synthesis gas.

To illustrate this effect, the stoichiometric reaction occurring at thereformer 302 and using steam 310 as an oxidant may be representedgenerally as follows:

—CH_(n)—+H₂O→CO+(1+n/2)H₂

At the fuel cell 304, the synthesis gas 312 is converted to electricity,carbon dioxide, and water in accordance with the following equation:

CO+2H₂+(3/2)O₂→CO₂+2H₂O+6e⁻

As can be observed from the above equations, each CH₂ group generates6e⁻ of electricity, which constitutes a 50 percent increase over the 4e⁻generated by the partial oxidation process described in FIG. 1.

In general, a solid oxide fuel cell converts about 50 percent of theheating value of the synthesis gas 312 to electricity and the other 50percent to heat. Because only about 30 percent of the heating value isneeded to reform the feedstock fuel 308 to synthesis gas 312, a solidoxide fuel cell produces sufficient heat 306 to provide the necessaryheat of reformation to the reformer 302. Nevertheless, even where theheat 306 generated by a fuel cell 304 is insufficient to provide therequired heat of reformation, the heat 306 may be supplemented by othersources (e.g., by partially combusting the feedstock fuel or using othersources of waste heat) until it is sufficient. In this way, anysignificant amount of heat 306 generated by the fuel cell 304 may berecycled, rather than wasted, to improve the efficiency of the reformer302.

Referring to FIG. 4, in selected embodiments, a plasma reformer 302 inaccordance with the invention may include a preheat zone 400, a plasmagenerator 402, and a reaction zone 404. The preheat zone 400 may be usedto preheat the reactants 308 to provide the required heat ofreformation. Because the reformation reaction is endothermic, thereactants 308, 310 may be heated in order to generate the desiredsynthesis gas 312. The reactants may include feedstock fuel and anoxidant. In one embodiment, the oxidant is at least one oxidant chosenfrom steam, oxygen, air, or some other oxygen-containing compound ormixture. Accordingly, the oxidant may include steam or oxygen or air oroxygen-containing compounds or oxygen-containing mixtures alone or incombination with each other. Where partial oxidation is used to providepart of the heat of reformation, the oxidant 108 may be provided insub-stoichiometric amounts to partially oxidize the feedstock fuel. Itwill be appreciated by those of skill in the art that whenstoichiometric amounts of reactants are provided for a reaction, theyare provided in a ratio such that substantially all of the reactants areconsumed by the reaction. When sub-stoichiometric amounts of reactantsare provided for a reaction, the reactants are not completely consumedby the reaction.

The thermodynamics of the reaction are such that synthesis gasproduction starts to increase at about 400° C. and maximizes at about800° C. Thus, the reactants may be heated to a temperature at or around800° C. to maximize synthesis gas production. The reactants 308, 310 maybe preheated somewhere near this temperature when they pass through theplasma generator 402, which acts as a catalyst to initiate thereformation reaction. In selected embodiments, only the steam 310 (aswell as air or oxygen mixed with the steam) is preheated. The feedstockfuel 308 may be mixed with the steam 310 just prior to passing throughthe plasma generator 402 (as indicated by the dotted line 406). This mayprevent the feedstock fuel 308 from becoming too hot, thermallydecomposing, and clogging up the system.

The preheat zone 400 may also be used to vaporize (i.e., convert to gasor mist) the reactants 308, 310 prior to routing them through the plasmagenerator 402. Reactants 308, 310 in a solid or liquid form may provideclusters of condensed matter which may act as nucleation sites. This maycause solid carbon nucleation which, although unavoidable, may bereduced by vaporizing the reactants 308, 310. In some cases, however,the reformer 302 may be used to process a feedstock fuel having agreater solid fraction. For example, a feedstock fuel such as a coalwater slurry (i.e., coal dust entrained in water) or coal dust suspendedin gas, which may have an energy content similar to jet fuel, may bevaporized as much as possible prior to being passed to the plasmagenerator 402. Nevertheless, feedstock fuels in pure gas form (e.g.,natural gas, biogas, etc.) may be less susceptible to carbon formation.

Once preheated, the reactants 308, 310 may be passed to the plasmagenerator 402 to ionize or break apart one or more of the reactants 308,310 to create reactive species. As will be explained in more detailhereafter, in selected embodiments, the plasma generator 402 may ionizethe reactants 308, 310 with a gliding electrical arc. This gliding arcmay provide the function of a physical catalyst by activating andinitiating the reformation reaction. However, the gliding arccontinually renews the active species whereas a physical catalyst relieson surface energy that can be “poisoned” by absorption of sulfur orbuildup of carbon on the surface. The energy used to generate thegliding electric arc may be on the order of 2 percent of the heatingvalue of the fuel 308 being processed. If a fuel cell 304 is 50 percentefficient (i.e., converts 50 percent of the fuel's electrical potentialto electricity), then only 4 percent of the fuel cell's electricity maybe used to operate the plasma generator 402. This represents anefficiency improvement over partial oxidation techniques, which mayconsume 30 percent or more of the fuel's current producing ability whenthe fuel is reformed by partial oxidation.

After ionization, the reactants may be passed to a reaction zone 404 toabsorb additional heat of reformation and complete the endothermicreactions. As vaporized reactants and products of the reactants leavethe plasma generator 402, some packets of gas may be oxygen rich whileothers may be oxygen lean. To further complete the reaction, thereactants may be physically mixed or homogenized by passing them througha chemical buffering compound, such as a solid state oxygen storagecompound. Here, the storage compound may absorb oxygen from oxygen-richpackets while releasing oxygen to oxygen-lean packets. This providesboth spatial and temporal mixing of the reactants to help the reactionprogress toward completion.

In other embodiments, the reaction zone 404 may contain catalystssuitable for promoting equilibration of gas species at temperaturesdifferent than the reforming reaction. That is, the temperature of thesynthesis gas produced in the reaction zone 404 may be reduced and otherreactions may be initiated. For example, the synthesis gas may be usedto produce methane within the reaction zone 404. Similarly, thesynthesis gas may be “shifted” to produce more hydrogen at the expenseof carbon monoxide. This may be performed, for example, by passing thesynthesis gas over an iron catalyst at temperatures below 400° C. Inother embodiments, the reaction zone 404 may also be used to coolreaction products leaving the reformer 302.

Referring to FIGS. 5A through 5C, in selected embodiments, a plasmagenerator 402 in accordance with the invention may include a pair ofelectrodes 500 a, 500 b having a large electrical voltage differencetherebetween (e.g., 6 kV). A preheated vapor stream containing thereactants 308, 310 may be directed between the electrodes 500 a, 500 bin the direction 502. The high voltage ionizes the gas which allowscurrent to flow, creating an arc 504 a, as shown in FIG. 5A. Because theions are in an electric field having a high potential (voltage)gradient, the ions begin to accelerate toward one electrode 500 a or theother 500 b depending on their charge. This provides tremendous kineticenergy for initiating the reformation reaction in addition to providingmeans for ionizing the reactants or simply breaking the reactants intoradicals to create more reactive species. Thus, in one embodiment, aplasma generator is provided to apply an electrical potential to thereactants sufficient to ionize one or more of the reactants. It will beappreciated by those of skill in that art that sufficient ionizationdepends upon factors including without limitation choice of electrodes,spacing of electrodes, gas flow, and pressure. A portion of thereactants is sufficiently ionized if the plasma can conduct anelectrical current.

Under the influence of the flowing gas, the ionized particles are sweptdownstream in the direction 502, with the ionized particles forming theleast resistive path for the current to flow. As a result, the arc 504 amoves downstream and spreads out as it follows the contour of theelectrodes 500 a, 500 b, as shown in FIG. 5B. Eventually, the gapbecomes wide enough that the current ceases to flow. The ionizedparticles, however, continue to move downstream. Once the current stopsflowing, the potential builds up on the electrodes 500 a, 500 b until itonce again ionizes the gas flowing therebetween. This creates a new arc504 b at a narrower region between the electrodes 500 a, 500 b, as shownin FIG. 5C. This process then repeats itself. Most of the endothermicreformation reaction may actually occur in the plasma area (i.e., thearea between the electrodes 500 a, 500 b) or immediately downstream fromthe plasma area.

Referring to FIG. 6, in order to provide heat of reformation to thereformer 302, a design may provide adequate heat transfer to the preheatzone 400, plasma generator 402, and reaction zone 404 of the reformer302. In selected embodiments, the reformer 302 and a fuel cell 304 maybe placed inside a furnace 600 or other insulated enclosure 600 in orderto retain heat and effectively transfer heat between the two components302, 304. In this embodiment, heat generated by the fuel cell 304, whichmay include heat generated through electrical resistance as well as heatgenerated electrochemically, may be transferred to the reformer 302through radiation, convection, or a combination thereof.

Accordingly, instead of insulating the reformer 302 to retain heat, thereformer 302 may be designed to conduct heat through an exterior wallwhere it may be transferred to internal components and fluids. Incertain embodiments, residual synthesis gas or other fuel in the exhaustof the fuel cell 304 may be burned to provide additional heat to thereformer 302. In other contemplated embodiments, heat may be transferredto the reformer 302 using a heat exchanger, such as a counter currentheat exchanger. This may be used, for example, to preheat steam used bythe reformer 302 with steam generated by the fuel cell 304.

In selected embodiments, the reformer 302 and fuel cell 304 may includea “cold” or reduced temperature region 602 a, 602 b. This enables pipesor wires to be more easily connected or disconnect to the reformer 302or fuel cell 304 in a region of reduced temperature. Accordingly,channels for conveying the feedstock fuel, air and steam, synthesis gas,and the like, as well as wires for conducting electricity may beconnected to the reformer 302 and fuel cell 304 in the reducedtemperature regions 602 a, 602 b.

Referring to FIG. 7, in one embodiment, a reformer 302 provides heattransfer to the reactants by way of an outer shell 700 to absorb heatradiated or otherwise conveyed from a fuel cell 304 or other externalheat source. The outer shell 700 may be made of steel or other materialshaving sufficient strength and stability at temperatures exceeding 800°C. In addition to providing a heat transfer mechanism to conduct heat tothe reactants 308, 310, the outer shell 700 provides a gas containmentenvelope that keeps the reactants 308, 310 as well as the products ofthe reactants (e.g., synthesis gas) isolated from the externalenvironment. It will be appreciated by those of skill in the art that aheat transfer mechanism may be anything that allows heat to transfer byradiation, convection, and/or conduction between the heat source and thereformation zone where an endothermic reaction can take place. A heattransfer mechanism may include without limitation, a surface areasituated between the heat source and the endothermic reaction zone thatallows heat to flow into the reaction zone. The surface area may beintegral with a vessel wall. In one embodiment, the surface area thatfunctions as a heat transfer mechanism is the surface area of theconduit that conveys reactants to the reaction zone.

A first channel 702 may be used to convey a mixture of air and steam 310into the reformer 302. In certain embodiments, the channel 702 mayoriginate in a low temperature region 602 a of the reformer 302 andtravel through a hot region 704 to preheat and further vaporize the airand steam 310. In selected embodiments, the channel 702 may be coupledto a coil 706 to provide additional surface area to further preheat theair and steam and vaporize the water 310. The coil 706 may be coupled toa channel 708 to convey the preheated air and steam 310 into anelectrically insulated region, such as the inside of an electricallynon-conductive tube 710. The non-conductive tube 710 may be made of amaterial such as an alumina ceramic and may prevent electricity fromdischarging from the plasma generator 402 to the conductive outer shell700, channels 702, 708, or other conductive surfaces.

Once the air and steam 310 are preheated, it may be mixed with afeedstock fuel conveyed through a feed channel 712. In selectedembodiments, this may occur within a mixing manifold 718 inside thenon-conductive tube 710. Where the feedstock fuel is a liquid or solid,the air and steam 310 may be preheated sufficiently to vaporize thefeedstock fuel 308 as it mixes with the air and steam 310. Thispreheated mixture is then introduced at some velocity between theelectrodes 500 a, 500 b of the plasma generator 402 where it is ionizedor broken into radicals to create more reactive species and therebyinitiate the reformation reaction. The electrodes 500 a, 500 b may beconnected to current-carrying conductors 720 a, 720 b connected to avoltage source outside of the reformer 302. In the plasma area and thearea immediately thereafter, most of the reactants may be converted tosynthesis gas.

In one embodiment, the reformer 302 includes a co-axial inner zonedefined by an inner surface of tube 710. The inner zone may contain theplasma generator 402. The reformer also includes an outer annulusdefined by the outer surface of the tube 710 and the inner surface ofthe outer shell 700. In this embodiment, the outer annulus contains thereaction zone 404. It will be appreciated by those of skill in the artthat a number of configurations may be provided to preheat the oxidantand/or feedstock fuel. The reformer need not have coaxial or annularzones. For example, in one embodiment, a long tube without a separateannular zone may be utilized where the conduit 708 is affixed outside orwithin the shell 710. The coils 706 or conduit may also be positionedwithin the shell 700 in a zone that is collinear with the plasmagenerator 402.

The synthesis gas and any residual reactants may then be conveyedthrough the non-conductive tube 710 and into an annular reaction zone404, where residual reactants may absorb additional heat of reformationand continue to react to form synthesis gas or other desired products.Here, the reactants may be homogenized by passing them through a packbed of chemical buffering compounds, such as the solid state oxygenstorage compound (such as for example CeO₂, NiO, CeO₂—ZrO₂, solids ofthese compounds or mixtures thereof) to promote further reaction. Thepack bed may also serve to physically mix the reactants. In selectedembodiments, the reactants and the products of the reactants may also bepassed over catalysts suitable for promoting equilibration of gasspecies at temperatures different than the reforming reaction.

The resulting products of reaction (e.g., synthesis gas) and anyresidual reactants (e.g., hydrocarbons, steam, oxygen, etc.) as well asnitrogen from the air may be collected through a port, such as aring-shaped collection manifold 714 or other suitable collection devicedisposed within the annular reaction zone 404. This fuel mixture maythen be conveyed through a channel 716 where it may be transmitted to afuel cell 304 for use as fuel. In selected embodiments, the annularregion beneath the collection manifold 714 may be filled with aninsulating material to maintain a temperature differential between thelow temperature zone 602 a and the hot zone 704.

FIGS. 8A through 8C show several perspective and cutaway perspectiveviews of one embodiment of a reformer 302 working in accordance with theprinciples described in association with FIG. 7. FIG. 8A shows oneembodiment of an outer shell 700 having a flange 800 mountable to afurnace or other surface. A second flange 802 may be attached to many ofthe reformer's internal components, allowing them to be removed from theouter shell 700 without removing or detaching the outer shell 700.Channels 702, 716 may be used to convey reactants and the products ofreactants to and from the reformer 302.

FIG. 8B shows a cutaway view of the outer shell 700, the innernon-conductive tube 710, and the coil 706. Also shown is a channel 708to convey preheated air and steam through a wall of the non-conductivetube 710 into the insulated core of the tube 710. Also shown is aring-shaped collection manifold 714 to collect synthesis gas and otherresidual materials from the annular reaction zone 404. FIG. 8C showsvarious internal components of the reformer 302 with the outer shell 700removed, including the non-conductive tube 710, the coil 706, thechannels 702, 708, and the collection manifold 714.

FIGS. 9A and 9B show several perspective views of embodiments of themixing manifold 718, collection manifold 714, channels 702, 708, andflanges 800, 802, with the outer shell 700 and non-conductive tube 710removed. As shown, in one embodiment, the mixing manifold 718 may besustained by several support bars 900 connected to a bottom mountingplate 902. The bottom mounting plate 902 may also be provided withapertures 904 to accommodate the current-carrying conductors 720 a, 720b illustrated in FIG. 7.

In addition to carrying current, the conductors 720 a, 720 b may act assupports for the electrodes 500 a, 500 b. These conductors 720 a, 720 bmay pass through cutout regions 906 of the mixing manifold 718, withouttouching the manifold 718, to support the electrodes 500 a, 500 b at aposition above the manifold 718. In the apertures 904, the conductors720 a, 720 b may be surrounded by high voltage insulators which preventelectricity from discharging to the mounting plate 902, while allowingthe conductors 720 a, 720 b to pass through the plate 902.

In selected embodiments, the mounting plate 902 may be removed from theflanges 800, 802 to remove the mixing manifold 718 and electrodes 500 a,500 b from the reformer assembly 302 while leaving the rest of thereformer 302 in place. In selected embodiments, one or more notches 908may be formed in the mounting plate 902 to ensure proper alignment, forexample, of the mixing manifold 718 with the channel 708.

Referring to FIG. 10, although particular reference has been made tofuel cells 104 herein, a reformer 302 in accordance with the inventionmay be used to improve the efficiency of other devices, systems, orprocesses that generate heat as a byproduct. For example, the reformer302 may be used in conjunction with a Fischer-Tropsch or methanationprocess 1000 to create synthetic fuel 1002 using synthesis gas 312 as aninput. As was described in association with FIG. 3, using steam as anoxidant (in place of oxygen) may produce synthesis gas with a hydrogento carbon monoxide ratio of roughly two to one. This ratio provides agood synthesis gas input to a Fischer-Tropsch process 1000.

A Fischer-Tropsch process 1000 may include chemically reacting synthesisgas (i.e., carbon monoxide and hydrogen) in the presence of a catalystto produce various types of liquid hydrocarbons. After extracting theliquid hydrocarbons, a tail gas may remain which may include a mixtureof water vapor, carbon dioxide, methane, nitrogen, unreacted synthesisgas, as well as residual vapor hydrocarbon products. The tail gas may berecycled back to a gasification unit or to a Fischer-Tropsch reactorinlet or may be burned as fuel.

In selected embodiments, the tail gas may be burned to provide heat 1004to a plasma reformer 302 in accordance with the invention. As previouslydescribed, this may allow steam to be used as the oxidant and mayincrease synthesis gas 312 production without requiring additional fuel1006 at the reformer input. Furthermore, this provides synthesis gaswith an improved hydrogen to carbon monoxide ratio (e.g., 2:1) forsynthetic fuel production. Thus, a plasma reformer 302 in accordancewith the invention may be used to improve synthetic fuel production whenintegrated with a Fischer-Tropsch process 1000.

The present invention may be embodied in other specific forms withoutdeparting from its essence or essential characteristics. The describedembodiments are to be considered in all respects only as illustrative,and not restrictive. The scope of the invention is, therefore, indicatedby the appended claims, rather than by the foregoing description. Allchanges within the meaning and range of equivalency of the claims are tobe embraced within their scope.

1. A reformer comprising: a channel to convey a preheated plurality ofreactants comprising a feedstock fuel and an oxidant; a plasma generatorto apply an electrical potential to the reactants sufficient to ionizeat least a portion of the reactants; a reaction zone to chemicallytransform the ionized reactants into synthesis gas comprising a mixtureof hydrogen and carbon monoxide; and a heat transfer mechanism totransfer heat utilized in a reformation reaction from an external heatsource to at least one destination chosen from the preheated reactants,the plasma generator, and the reaction zone.
 2. The reformer of claim 1,wherein the feedstock fuel comprises at least one of a hydrocarbon andcarbon.
 3. The reformer of claim 1, wherein the preheated reactantscomprise a vapor.
 4. The reformer of claim 1, wherein the oxidantcomprises at least one oxidant chosen from steam, air, oxygen,oxygen-containing compound and oxygen-containing mixtures.
 5. Thereformer of claim 1, wherein the feedstock fuel comprises at least onefuel chosen from a gas, a liquid, and a solid.
 6. The reformer of claim1, wherein the plasma generator comprises a gliding electric arcsufficient to ionize at least a portion of the reactants.
 7. Thereformer of claim 1, wherein the reaction zone comprises a reaction bedeffective to homogenize at least a portion of the reactants by mixing.8. The reformer of claim 1, wherein the reaction zone comprises areaction bed effective to homogenize at least a portion of the reactantsby chemical buffering.
 9. The reformer of claim 1, wherein thetemperature of reformation is between about 350° C. and about 1100° C.10. The reformer of claim 8, wherein the reaction zone comprises areaction bed containing at least one catalyst to promote equilibrationof reactive species at temperatures lower than the temperature ofreformation.
 11. The reformer of claim 1, wherein the oxidant isprovided in sub-stoichiometric amounts to partially oxidize thefeedstock fuel.
 12. The reformer of claim 1, wherein the external heatsource comprises at least one source chosen from a solid-oxide fuelcell, a molten-carbonate fuel cell, a phosphoric acid fuel cell, amethanation reactor and a Fischer-Tropsch process.
 13. The reformer ofclaim 1, wherein the reformer and external heat source are each disposedwithin an insulated enclosure.
 14. The reformer of claim 1, furthercomprising a co-axial inner zone, containing the plasma generator, andan outer annulus, containing the reaction zone.
 15. The reformer ofclaim 1, further comprising a heating zone to heat the preheatedreactants.
 16. A thermally integrated system for producing electricityusing a feedstock fuel as an input, the system comprising: a plasmareformer configured to convert a mixture containing a feedstock fuel andan oxidant to a synthesis gas containing a mixture of hydrogen andcarbon monoxide gas, the conversion of the mixture comprising anendothermic reaction; a fuel cell to chemically convert the synthesisgas to electricity and heat; and a heat transfer mechanism to transferheat from the fuel cell to the plasma reformer to provide the heat forthe endothermic reaction.
 17. The system of claim 16, wherein thefeedstock fuel comprises at least one of a hydrocarbon and carbon. 18.The system of claim 16, wherein the mixture containing the feedstockfuel and the oxidant is preheated to create a vapor.
 19. The system ofclaim 16, wherein the oxidant comprises at least one oxidant chosen fromsteam, oxygen, oxygen-containing compounds, and oxygen-containingmixtures.
 20. The system of claim 16, wherein the feedstock fuelcomprises at least one fuel chosen from a gas, a liquid and a solid. 21.The system of claim 16, wherein the conversion of the mixture containingfeedstock fuel and an oxidant to a synthesis gas occurs in the range ofbetween about 350° C. and about 1100° C.
 22. The system of claim 16,wherein the conversion of the mixture containing feedstock fuel and anoxidant to a synthesis gas occurs in the range of between about 800° C.and about 950° C.
 23. The system of claim 16, wherein the oxidant isprovided in sub-stoichiometric amounts to partially oxidize thefeedstock fuel.
 24. The system of claim 16, wherein the fuel cellcomprises at least one fuel cell chosen from a solid-oxide fuel cell, amolten-carbonate fuel cell, and a phosphoric acid fuel cell.
 25. Thesystem of claim 16, wherein the plasma reformer and the fuel cell aredisposed within an insulated enclosure.
 26. The system of claim 25,wherein the fuel cell transfers heat to the plasma reformer by way ofradiation.
 27. The system of claim 25, wherein the fuel cell transfersheat to the plasma reformer by way of convection.
 28. A method forincreasing the Faradaic efficiency of a fuel cell, the methodcomprising: preheating a plurality of reactants comprising a feedstockfuel and an oxidant; applying an electrical potential to the reactantssufficient to ionize at least a portion of the reactants; chemicallytransforming the ionized reactants into synthesis gas comprising amixture of hydrogen and carbon monoxide while applying heat ofreformation; generating, using the synthesis gas as a fuel, electricityand heat; and transferring at least a portion of the heat to thereactants to provide the heat of reformation.
 29. The method of claim28, wherein preheating the plurality of reactants comprises preheatingthe reactants using the heat generated from the fuel cell.
 30. Themethod of claim 28, wherein the feedstock fuel comprises at least one ofa hydrocarbon and carbon.
 31. The method of claim 28, further comprisingvaporizing the reactants prior to applying the electrical potential. 32.The method of claim 28, wherein the oxidant comprises at least oneoxidant chosen from steam, oxygen, an oxygen-containing compound and anoxygen-containing mixture.
 33. The method of claim 28, wherein thefeedstock fuel comprises at least one fuel chosen from a gas, a liquid,and a solid.
 34. The method of claim 28, wherein applying an electricalpotential comprises ionizing the reactants with a gliding electric arc.35. The method of claim 28, wherein chemically transforming the ionizedreactants comprises homogenizing the reactants by mixing.
 36. The methodof claim 28, wherein chemically transforming the ionized reactantscomprises homogenizing the reactants by chemical buffering.
 37. Themethod of claim 28, wherein applying the heat of reformation comprisesheating the reactants to a temperature between about 350° C. and 1100°C.
 38. The method of claim 28, wherein applying the heat of reformationcomprises heating the reactants to a temperature between about 800° C.and 950° C.
 39. The method of claim 28, wherein transferring at least aportion of the heat to the reactants comprises transferring heat to thereactants by way of at least one of radiation and convection.